Container handling vehicle with direct drive on lifting axle(s), associated methods and system

ABSTRACT

An automated storage and retrieval system includes a plurality of stacks of storage containers arranged in storage columns, and a container handling vehicle. The container handling vehicle includes a transport mechanism for transport of the vehicle, and a lifting assembly for picking up storage containers from the storage columns. The lifting assembly includes: a lifting frame connectable to a storage container, a first lifting shaft and a second lifting shaft, the first and second lifting shafts being mainly parallel, and each of the first and second lifting shafts being supported in an upper portion of the vehicle, two lifting elements extending from each of the first and second lifting shafts to the lifting frame, and a motor drive assembly having at least one motor including a first motor, and a force transferring assembly rotatably connecting the first and second lifting shafts via a force transferring element.

The present invention relates to an automated storage and retrievalsystem, a container handling vehicle which can operate on an automatedstorage and retrieval system, and a method of operating an automatedstorage and retrieval system.

BACKGROUND AND PRIOR ART

FIG. 1 discloses a framework structure 1 of a typical prior artautomated storage and retrieval system and FIGS. 2A-2C disclosedifferent container handling vehicles 9 of such a system.

The framework structure 1 comprises a plurality of upright members 2 anda plurality of horizontal members 3, which are supported by the uprightmembers 2. The members 2, 3 may typically be made of metal, e.g.extruded aluminium profiles.

The framework structure 1 defines a storage grid 4 comprising storagecolumns 5 arranged in rows, in which storage columns 5 store storagecontainers 6, also known as bins, are stacked one on top of another toform stacks 7. Each storage container 6 may typically hold a pluralityof product items (not shown), and the product items within a storagecontainer 6 may be identical, or may be of different product typesdepending on the application. The framework structure 1 guards againsthorizontal movement of the stacks 7 of storage containers 6, and guidesvertical movement of the containers 6, but does normally not otherwisesupport the storage containers 6 when stacked.

A rail system 8 is arranged in a grid pattern across the top of thestorage columns 5, on which rail system 8 a plurality of containerhandling vehicles 9 are operated to raise storage containers 6 from andlower storage containers 6 into the storage columns 5, and also totransport the storage containers 6 above the storage columns 5. The railsystem 8 comprises a first set of parallel rails 10 arranged to guidemovement of the container handling vehicles 9 in a first direction Xacross the top of the frame structure 1, and a second set of parallelrails 11 arranged perpendicular to the first set of rails 10 to guidemovement of the container handling vehicles 9 in a second direction Y,which is perpendicular to the first direction X. In this way, the railsystem 8 defines grid columns 12 above which the container handlingvehicles 9 can move laterally above the storage columns 5, i.e. in aplane which is parallel to the horizontal X-Y plane.

Each container handling vehicle 9 comprises a vehicle body 13 and firstand second sets of wheels 14, 15 which enable the lateral movement ofthe container handling vehicle 9, i.e. the movement in the X and Ydirections. In FIG. 2A two wheels in each of the sets 14, 15 arevisible, while in FIGS. 2B and 2C only two wheels in one of the set ofwheels 14 are visible. The first set of wheels 14 is arranged to engagewith two adjacent rails of the first set 10 of rails, and the second setof wheels 15 arranged to engage with two adjacent rails of the secondset 11 of rails. Each set of wheels 14, 15 can be lifted and lowered, sothat the first set of wheels 14 and/or the second set of wheels 15 canbe engaged with the respective set of rails 10, 11 at any one time.

Each container handling vehicle 9 also comprises a lifting device 16(see FIGS. 2B and 2C) for vertical transportation of storage containers6, e.g. raising a storage container 6 from and lowering a storagecontainer 6 into a storage column 5. The lifting device may be arrangedinside the body 13 (as in FIG. 2A) or outside the body 13 (as disclosedin FIGS. 2B and 2C). The lifting device 16 may comprise a lifting frame18 which is adapted to engage a storage container 6, which lifting frame18 can be lowered from the vehicle body 13 so that the position of thelifting frame with respect to the vehicle body 13 can be adjusted in athird direction Z, which is orthogonal the first direction X and thesecond direction Y.

Conventionally, and also for the purpose of this application, Z=1identifies the uppermost layer of the grid 4, i.e. the layer immediatelybelow the rail system 8, Z=2 the second layer below the rail system 8,Z=3 the third layer etc. In the embodiment disclosed in FIG. 1 , Z=8identifies the lowermost, bottom layer of the grid 4. Consequently, asan example and using the Cartesian coordinate system X, Y, Z indicatedin FIG. 1 , the storage container identified as 7′ in FIG. 1 can be saidto occupy grid location or cell X=10, Y=2, Z=3. The container handlingvehicles 9 can be said to travel in layer Z=0 and each grid column canbe identified by its X and Y coordinates.

Each container handling vehicle 9 comprises a storage compartment orspace for receiving and stowing a storage container 6 when transportingthe storage container 6 across the grid 4. The storage space maycomprise a cavity arranged centrally within the vehicle body 13 (FIG.2A), e.g. as is described in WO2014/090684A1, the contents of which areincorporated herein by reference. Alternatively, the storage compartmentor space can be arranged on the side of the body as disclosed in FIGS.2B and 2C, i.e. the container handling vehicles may have a cantileverconstruction, as is described in U.S. Pat. No. 317,366, the contents ofwhich are also incorporated herein by reference.

The container handling vehicles 9 may have a footprint 22 (see FIG. 4 ),i.e. an extent in the X and Y directions, which is generally equal tothe lateral or horizontal extent of a grid column 12, i.e. the extent ofa grid column 12 in the X and Y directions, e.g. as is described inWO2015/193278A1, the contents of which are incorporated herein byreference. Alternatively, the container handling vehicles 9 may have afootprint which is larger than a lateral extent of a grid column 12,e.g. as is disclosed in WO2014/090684A1.

The rail system 8 may be a single rail system, as is shown in FIG. 3 .Alternatively, the rail system 8 may be a double rail system, as isshown in FIG. 4 , thus allowing a container handling vehicle 9 having afootprint 22 generally corresponding to the lateral extent of a gridcolumn 12 to travel along a row of grid columns even if anothercontainer handling vehicle 9 is positioned above a grid columnneighbouring that row.

In a storage grid, a majority of the grid columns 12 are storage columns5, i.e. grid columns where storage containers are stored in stacks.However, a grid normally has at least one grid column which is used notfor storing storage containers, but which comprises a location where thecontainer handling vehicles can drop off and/or pick up storagecontainers so that they can be transported to an access station wherethe storage containers can be accessed from outside of the grid ortransferred out of or into the grid. Within the art, such a location isnormally referred to as a “port” and the grid column in which the portis located may be referred to as a port column.

The grid 4 in FIG. 1 comprises two port columns 19 and 20. The firstport column 19 may for example be a dedicated drop-off port column wherethe container handling vehicles 9 can drop off storage containers to betransported to an access or a transfer station (not shown), and thesecond port 20 column may be a dedicated pick-up port column where thecontainer handling vehicles 9 can pick up storage containers that havebeen transported to the grid 4 from an access or a transfer station.

The access station may typically be a picking or a stocking stationwhere product items are removed from or positioned into the storagecontainers. In a picking or a stocking station, the storage containersare normally never removed from the automated storage and retrievalsystem, but are returned back into the grid once accessed. A port canalso be used for transferring storage containers out of or into thegrid, e.g. for transferring storage containers to another storagefacility (e.g. to another grid or to another automated storage andretrieval system), to a transport vehicle (e.g. a train or a lorry), orto a production facility.

A conveyor system comprising conveyors is normally employed to transportthe storage containers between the ports and the access station.

If the port and the access station are located at different levels, theconveyor system may comprise a lift device for transporting the storagecontainers vertically between the port and the access station.

The conveyor system may be arranged to transfer storage containersbetween different grids, e.g. as is described in WO2014/075937A1, thecontents of which are incorporated herein by reference.

WO2016/198467A1, the contents of which are incorporated herein byreference, disclose an example of a prior art access system havingconveyor belts (FIGS. 5 a and 5 b in WO2016/198467A1) and a framemounted track (FIGS. 6 a and 6 b in WO2016/198467A1) for transportingstorage containers between ports and work stations where operators canaccess the storage containers.

When a storage container 6 stored in the grid 4 disclosed in FIG. 1 isto be accessed, one of the container handling vehicles 9 is instructedto retrieve the target storage container from its position in the grid 4and transport it to the drop-off port 19. This operation involves movingthe container handling vehicle 9 to a grid location above the storagecolumn in which the target storage container is positioned, retrievingthe storage container from the storage column using the containerhandling vehicle's lifting device (not shown), and transporting thestorage container to the drop-off port 19. If the target storagecontainer 6 is located deep within a stack 7, i.e. with one or aplurality of other storage containers positioned above the targetstorage container, the operation also involves temporarily moving theabove-positioned storage containers prior to lifting the target storagecontainer from the storage column. This step, which is sometimesreferred to as “digging” within the art, may be performed with the samecontainer handling vehicle 9 that is subsequently used for transportingthe target storage container to the drop-off port 19, or with one or aplurality of other cooperating container handling vehicles 9.Alternatively, or in addition, the automated storage and retrievalsystem may have container handling vehicles 9 specifically dedicated tothe task of temporarily removing storage containers 6 from a storagecolumn. Once the target storage container has been removed from thestorage column, the temporarily removed storage containers 6 can berepositioned into the original storage column. However, the removedstorage containers 6 may alternatively be relocated to other storagecolumns.

When a storage container 6 is to be stored in the grid 4, one of thecontainer handling vehicles 9 is instructed to pick up the storagecontainer from the pick-up port 20 and transport it to a grid locationabove the storage column where it is to be stored. After any storagecontainers 6 positioned at or above the target position within thestorage column stack have been removed, the container handling vehicle 9positions the storage container 6 at the desired position. The removedstorage containers may then be lowered back into the storage column, orrelocated to other storage columns.

For monitoring and controlling the automated storage and retrievalsystem, e.g. monitoring and controlling the location of respectivestorage containers within the grid 4, the content of each storagecontainer 6, and the movement of the container handling vehicles 9 sothat a desired storage container can be delivered to the desiredlocation at the desired time without the container handling vehicles 9colliding with each other, the automated storage and retrieval systemcomprises a control system, which typically is computerised andcomprises a database for keeping track of the storage containers.

Furthermore, in the prior art lifting systems for container handlingvehicles, the lifting assembly comprise a mechanical motor, mechanicallyconnected to two separate lifting shafts via a gear and beltarrangement. The mechanical parts will, over time, be subject to wearand tear resulting in uneven/skewed lifting of the storage containers.

It is thus an objective of the invention to provide a lifting system forthe container handling vehicle which provides for a more stable lift ofthe storage containers or storage bins.

More specifically, it is an objective of the present invention toprovide a lifting system for container handling vehicle where thelifting operation provides for minimum relative movement of thedifferent lifting bands connected to a lifting frame to ensure that thestorage container or storage bin is kept levelled with a planesubstantially parallel with a horizontal plane during the entirevertical lifting operation.

It is a further objective of the invention to be less dependent onmechanical parts in the lifting system as the mechanical parts aresusceptible to wear and tear.

SUMMARY OF THE INVENTION

The invention is set forth in the independent claims and the dependentclaims describe alternatives of the invention.

The invention relates to an automated storage and retrieval systemcomprising:

-   -   a rail system comprising a first set of parallel tracks arranged        in a horizontal plane and extending in a first direction, and a        second set of parallel tracks arranged in the horizontal plane        and extending in a second direction which is orthogonal to the        first direction, which first and second sets of tracks form a        grid pattern in the horizontal plane comprising a plurality of        adjacent grid cells, each comprising a grid opening defined by a        pair of neighboring tracks of the first set of tracks and a pair        of neighboring tracks of the second set of tracks; and    -   a plurality of stacks of storage containers arranged in storage        columns located beneath the rail system, wherein each storage        column is located vertically below a grid opening;    -   a container handling vehicle comprising:    -   a transport mechanism for transport of the vehicle on the rail        system,    -   a lifting assembly for picking up storage containers from the        storage columns to a position above the lowest level of the        transport mechanism,    -   wherein the lifting assembly comprises:    -   a lifting frame connectable to a storage container,    -   a first lifting shaft and a second lifting shaft of equal or        near equal diameter, the first and second lifting shafts being        mainly parallel, and each of the first and second lifting shafts        being supported in an upper portion of the vehicle, two lifting        elements extending from each of the lifting shafts to the        lifting frame,    -   a motor drive assembly comprising at least one motor, wherein        the at least one motor encircles one of the lifting shafts, and    -   a force transferring assembly rotatably connecting the first and        second lifting shafts via a force transferring element.

The first and second lifting shafts are preferably of equal or nearequal diameter. This provides for a similar angular velocity of thereeling surfaces on the first and second lifting shafts when the liftingshafts are rotated, and results in that the lifting frame issubstantially levelled during lifting and lowering (i.e. the liftingframe is parallel with horizontal planes during lifting and lowering).

The force transferring element of the force transferring assembly can beseen as a timing belt, which ensures that the first and second liftingshafts are synchronized. Alternatively, the force transferring elementcomprises a driving belt. Alternatively, the force transferring assemblymay comprise a belt in the form of a chain. Thus, the force transferringelement can be any synchronizing device that ensures that the angularvelocities of the reeling surfaces of the first and second liftingshafts are matched, thereby the lifting frame is evenly lifted, i.e. thelifting frame is substantially parallel with a horizontal plane duringlifting and lowering.

Common to all the aspects of the system is the presence of:

-   -   a first and second lifting shaft wheel whereof each is connected        for rotation with the respective lifting shaft,    -   at least one other guide wheel,    -   a force transferring element forming a closed loop, and    -   at least one of the other guide wheels is arranged inside the        closed loop,    -   the first or second lifting shaft wheel is in contact with an        inner surface of the force transferring element, and    -   the other of said first or second shaft is in contact with an        outer surface of the force transferring element. In other words,        one of the first or second lifting shaft wheels is arranged        inside the closed loop formed by the force transferring element        and the other of the first or second lifting shaft wheel is        arranged outside the closed loop formed by the force        transferring element. Such setup results in opposite rotation of        the first lifting shaft relative the second lifting shaft.

One electric motor may be arranged around one of the lifting shaftsproviding power transfer, i.e. a rotational movement, to the liftingshaft. In one aspect, the lifting shaft may form an integral part of theelectric motor.

In an aspect, the force transferring element comprises an endless beltwith an inner surface and an outer surface and wherein the first liftingshaft is in contact with the inner surface or the outer surface of thebelt and the second lifting shaft is in contact with the other of saidinner surface or outer surface of the belt. Alternatively, the forcetransferring element can comprise a Mobius strip. In all aspects, theforce transferring assembly is configured such that the first and secondlifting shafts rotate in opposite directions.

Thus, the force transferring assembly is arranged in a configurationrendering possible the opposite rotation, i.e. counter rotation, of thefirst lifting shaft relative the second lifting shaft.

The force transferring assembly may comprise a first lifting shaft wheelconnected for rotation with the first lifting shaft and a second liftingshaft wheel connected for rotation with the second lifting shaft and atleast one guide wheel urging the outer surface of the belt against oneof the first or second lifting shaft wheels, such that when one of thefirst or second lifting shaft moves in a first rotational direction theother of said first and second lifting shaft moves in a secondrotational direction opposite the first direction, in both rotationaldirections. This opposite rotation ensures that the lifting frame, andany storage container lifted by the lifting frame, is liftedsubstantially vertically with minimum horizontal movement during thevertical lifting operation. Preferably, the first and second liftingshafts and the lifting elements, are such connected that the liftingelements are reeled onto the lifting shafts from outside. This ensuresconnection of the lifting elements in end portions (e.g. in the cornersor close to the corners) of the lifting frame as well as it ensures thatthe lifting frame is centred and only moves in the vertical direction(no horizontal movement) relative the first and second lifting shaftsduring the entire lifting sequence.

The force transferring element may in one aspect form a closed loopwhere one of the first or second lifting shaft wheels is arranged insidethe closed loop and the other of the first or second lifting shaftwheels is arranged outside the closed loop. Such setup facilitates thearrangement of vertical keyhole shaped holes for mounting the shaftswhile allowing ease of maintenance too.

In an aspect, the force transferring assembly comprises a tensioning ortightening mechanism for initial tightening of the force transferringelement. The tensioning mechanism may comprise an eccentric tensioningmechanism comprising a tightening wheel with an axle that can beadjusted within an opening in a fixed bracket. Thus, the axle of thetightening wheel can be moved in different directions relative theopening in the fixed bracket. The area of the opening is thus largerthan an area occupied by the cross section of the axle within theopening in all positions of the axle within the opening. Such tensioningmechanism can be advantageous in order to further ensure that the forcetransferring assembly can provide synchronous operation of the first andsecond lifting shafts. The force transferring element is preferably of anon-elastic material such that the length of the force transferringelement is fixed. When the force transferring element is initiallyinstalled, proper tensioning is assured using a tuning fork measuringthe frequency of the force transferring element. The frequencycorresponds to a given tension. The tensioning in the force transferringelement is adjusted by moving the tightening wheel within the opening ofthe bracket, thereby the length of the force transferring element isadjusted and thus the tension in the force transferring element.

When the frequency of the force transferring element is within apredetermined frequency range, the tightening wheel is locked in thisposition by appropriate fastening elements such as screws or bolts etc.Once locked in dedicated position, the force transferring assembly (i.e.the force transferring element and the guide wheel(s) and/or tighteningwheel) is, in theory, adapted to operate for several thousands of hoursbefore it has to be changed, similar to a drive belt in a combustionengine in a car.

The tightening wheel of the tensioning mechanism may be a separate guidewheel from the guide wheels used in the counter rotation mechanism ofthe first and second lifting shafts, or may be one of the guide wheelsused for the counter rotation of the first and second lifting shafts.

In an aspect, the at least one motor comprises a brushless DC motor.Various types of brushless DC motors are known, including permanentmagnet synchronous motor (using permanent magnets) and switchedreluctance motors (does not use any permanent magnets).

The working principles of the permanent magnet synchronous brushless DCmotor is known to the skilled person, e.g. as described inhttps://en.wikipedia.org/wiki/Brushless_DC_electric_motor, and typicallyuses one or more permanent magnets in the rotor and electromagnets onthe motor housing for the stator. A motor controller converts DC to AC.This design is mechanically simpler than that of brushed motors becauseit eliminates the complication of transferring power from outside themotor to the spinning rotor. The motor controller can sense the rotor'sposition via Hall effect sensors or similar devices and can preciselycontrol the timing, phase, etc., of the current in the rotor coils tooptimize torque, conserve power, regulate speed, and even apply somebraking.

The working principles of switched reluctance motors are known to theskilled person and are described in for instance Jin-Woo Ahn (2011),Switched Reluctance Motor, Torque Control, Prof. Moulay Tahar Lamchich(Ed.), ISBN: 978-953-307-428-3, InTech, available from:http://cdn.intechweb.org/pdfs/13717.pdf and in R. Krishnan (2001),Switched reluctance motor drives: Modelling, Simulation, Analysis,Design and Applications; CRC Press.

In an aspect, the at least one motor comprises a rotary electrical motorconverting direct current electrical energy into rotational energy ofthe at least first or second lifting shafts.

In an aspect, the at least one motor is a permanent magnet brushless DCmotor, where the motor comprises a stator arranged radially betweenrotor magnets (on the radial outside of the stator) and the first orsecond lifting shaft (on the radial inside of the stator). The statormay be fixed to a stator housing, which stator housing is connected to ahousing of the container handling vehicle. The rotor magnets may bearranged on an inside of a wheel rim surrounding the stators and can beconnected to rotate with the first or second lifting shaft such that therotor magnets and the first or second lifting shafts rotates together.The stator(s) then rotates the rotor magnets and thereby the liftingshaft. The stator may, e.g. be arranged at least partly, preferablyfully, within the same rotational plane as a motor housing and at leastpartly, preferably fully, within the container vehicle body. The term“rotational plane” signifies in this embodiment the plane extendingperpendicular from the rotational axis of the lifting shafts. Saidstators include both windings and yoke, and the stator field windingsare following the outer periphery of wheel rim where the rotor magnetsare arranged.

In an aspect, the electric motor may be a reluctance motor with similarworking principles as the permanent magnet brushless DC motor describedabove, for instance a switched reluctance motor, comprising a statorelement with multiple stator poles and a rotor element featuringmultiple rotor poles, connected to, or being part of, a drive shaftwhere one of the lifting shafts is the rotor element, or forms part ofthe rotor element. The rotor element (or drive shaft) of the reluctancemotor may be aligned with the centerline of the lifting shaft orcomprise a part of one end of the lifting shaft. Alternatively, thestator element can be arranged within the rotor element (or vice versa),and the rotor element may be arranged within the lifting shaft, as apart of, or operationally connected to, said lifting shaft. This lattersolution will free a maximum amount of space within the cavity of thevehicle body.

In an aspect, the container handling vehicle comprises means suitablefor measuring (at least indirectly) electromotive force (emf) of atleast one of the lifting shafts, the means being in signal communicationwith one of the stator and the rotor, thereby allowing online rollingset specific velocity registration of the lifting operation duringlifting. For example, a back-emf measurement circuit may be installed insignal communication with at least one of the lifting shafts. A hallsensor may be used as an alternative or in combination.

In another aspect, the container handling vehicle further comprisesmeans suitable for measuring acceleration of at least one of the firstand second lifting shafts, the means being in signal communication withthe stator. Such a means comprises preferably one or more piezoelectricsensors, for example an accelerometer from PCB™ Piezotronics. One ormore inductive sensors may be used as an alternative to piezoelectricsensor(s), or in combination with piezoelectric sensor(s).

In an aspect, the motor drive assembly comprises a second motor whereinthe second motor encircles the same lifting shaft as the first motor,and wherein the force transferring assembly comprises a belttransferring torque from the first or second lifting shaft with thefirst and second motors to the other of the first or second liftingshaft.

In an aspect, the motor drive assembly comprises a second motorencircling the other of said first or second lifting shaft differentfrom the first motor, and wherein the force transferring assemblycomprises a timing belt providing synchronous movement of the first andsecond lifting shafts relative each other.

In an aspect, for example if using a first and second motor encirclingthe same lifting shaft or encircling respective first and second liftingshafts, the system further comprises sensing means, such as a sensor, ineach of the first and second motors providing input to an encoder ineach motor to determine the speed of each motor. Signals representingthe speed of each motor are transmitted to a common control system,which control system, based on the signals, operate the different motorsto increase or reduce their speed. This may for example be advantageousas an additional force transferring element in situations where the loadof a storage container is unequally distributed and the center ofgravity of the storage container is more to one side than another side(i.e. center of gravity is not in the geometric center of the bottom ofthe storage container) resulting in that the loads experienced by themotors are unequal. The sensor may for example read an optical discprovided with a number of data sources.

In an aspect, the force transferring arrangement is configured tosynchronize the rotation of the first lifting shaft and the secondlifting shaft.

In an aspect, a rotational force of the motor drive assembly correspondsto intended maximum weight of storage container with item. Such maximumweight may typically be from 2 to 50 kilograms.

In an aspect, the force transferring assembly comprises a number angulargears and a link shaft, wherein the angular gears are connected forrotation with each of the first and second lifting shafts and the linkshaft is arranged between the angular gears of the first and secondlifting gears.

The invention further relates to a container handling vehicle for movingstorage containers stacked in stacks within an automated storage andretrieval system, wherein the container handling vehicle is configuredto move on a rail system above storage columns and comprises:

-   -   a lifting assembly for picking up storage containers from the        storage columns to a position above the lowest level of the        transport mechanism on the container handling vehicle,        -   wherein the lifting assembly comprises:    -   a lifting frame connectable to a storage container,    -   a first lifting shaft and a second lifting shaft of equal or        near equal diameter, the first and second lifting shafts being        mainly parallel, each of the first and second lifting shafts        being supported in an upper portion of the vehicle,    -   two lifting elements extending from each of the first and second        lifting shafts to the lifting frame,    -   a motor drive assembly comprising at least a first motor,        wherein the at least first motor encircles one of the lifting        shafts, and    -   a force transferring assembly rotatably connecting the first and        second lifting shafts via a force transferring element. The        automated storage and retrieval system may comprise a rail        system comprising a first set of parallel tracks arranged in a        horizontal plane and extending in a first direction, and a        second set of parallel tracks arranged in the horizontal plane        and extending in a second direction which is orthogonal to the        first direction, which first and second sets of tracks form a        grid pattern in the horizontal plane comprising a plurality of        adjacent grid cells, each comprising a grid opening defined by a        pair of neighboring tracks of the first set of tracks and a pair        of neighboring tracks of the second set of tracks, and a        plurality of stacks of storage containers arranged in storage        columns located beneath the rail system, wherein each storage        column is located vertically below a grid opening.

In an aspect of the container handling vehicle, the force transferringassembly comprises an endless belt and a first lifting shaft wheelconnected for rotation with the first lifting shaft and a second liftingshaft wheel connected for rotation with the second lifting shaft and atleast one guide wheel arranged such that when one of the first or secondlifting shaft moves in a first rotational direction the other of saidfirst and second lifting shaft moves in a second rotational directionopposite the first direction. The endless belt forms a closed loop andone of the first or second lifting shaft wheels is arranged inside theclosed loop and the other of the first or second lifting shaft wheels isarranged outside the closed loop.

The container handling vehicle can have a central cavity or a cantileverconstruction for receiving storage containers.

It is further described use of a container handling vehicle as definedabove for storage and retrieval of storage containers in a storagesystem.

It is further described a method of operating an automated storage andretrieval system as defined above, comprising providing signals todifferent container handling vehicles operating in said system to storestorage containers in stacks and retrieve storage containers fromstacks.

The invention further relates to use of a container handling vehicle asdescribed above for storage and retrieval of storage containers in astorage system.

The invention further relates to a method of operating an automatedstorage and retrieval system as described above, comprising providingsignals to different container handling vehicles operating in saidsystem to store storage containers in stacks and retrieve storagecontainers from stacks.

The invention further relates to a method of operating a liftingassembly of a container handling vehicle comprising:

-   -   arranging a motor drive assembly comprising at least a first        motor to encircle a first or a second lifting shaft of the        lifting system,    -   connecting two lifting elements from each of the first and        second lifting shafts to a lifting frame,    -   rotationally coupling the first and second lifting shafts to        synchronize the raising and lowering of opposite sides of the        lifting frame,    -   using a lifting assembly for picking up storage containers from        storage columns to a position above the lowest level of the        transport mechanism on the container handling vehicle.

In an aspect of the method, the method further comprising:

-   -   encircling a second motor around the same first or second        lifting shaft as the first motor, or around the other of said        first or second lifting shaft as the first motor.

The lifting elements are preferable electrically and signally conductivesuch that grippers on the lifting frame can be electronically operatedto grip and hold storage containers. The lifting elements may be bandsor other electrically and signally conductive means.

The lifting shaft(s) is preferably provided with a brake arrangement.The brake arrangement can be arranged on an inside or outside of thecontainer vehicle housing and can be a locking pin cooperating with agear connected for rotation with the first or second lifting shaft, e.g.a ratchet mechanism. In a locked position of the locking arrangement,the locking pin is in engagement with the gear on the lifting shaft,thereby preventing rotation of the gear (and thus the lifting shaft). Inan open position of the locking arrangement, the locking pin is operatedto a position out of engagement with the gear on the lifting shaft,thereby the lifting shaft is free to rotate on any instructions from themotor(s).

Another advantage of the invention in view of the prior art solutionswhere the drive system for the lifting device is based on motorsconnected to the lifting shafts via gears is, in addition to a morereliable system with longer service intervals on the parts, a systemwhich is easier to assemble as the system comprises fewer parts and isless complex. Furthermore, as the motor operates directly on the atleast first and or second lifting shaft, a more efficient and accuratelifting is achieved as the lifting shaft(s) is instantaneouslyinfluenced by the motor(s).

In an aspect, the housing of the container handling vehicle is casted inone piece. The housing can e.g. be an Aluminum casing casted in onepiece. Normally, according to prior art solutions, a plurality of thinmetal plates are connected by screws or bolts. The one piece castingeliminates the need for the thin metal plates and thus reduces thenumber of screws used for connecting the plates (typically approximately40 screws are used for connecting the plates). In addition, the onepiece casting results in less time spent on assembling the containerhandling vehicles because there are less parts to assemble.

In an aspect, there may be four lifting elements in total, two from eachof the first and second lifting shafts.

In the following description, numerous specific details are introducedby way of example only to provide a thorough understanding ofembodiments of the claimed system, container handling vehicle andmethod. One skilled in the relevant art, however, will recognize thatthese embodiments can be practiced without one or more of the specificdetails, or with other components, systems, etc. In other instances,well-known structures or operations are not shown, or are not describedin detail, to avoid obscuring aspects of the disclosed embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

Following drawings are appended to facilitate the understanding of theinvention;

FIG. 1 is a perspective view of a grid with a rail system of a prior artautomated storage and retrieval system;

FIG. 2A is a perspective view of a first prior art container handlingvehicle;

FIG. 2B is a perspective view of a second prior art container handlingvehicle;

FIG. 2C is a side view of the second prior art container handlingvehicle in FIG. 2B, showing a lifting device, i.e. elevator, for liftingand or lowering storage containers;

FIG. 3 is a top view of a prior art single rail grid;

FIG. 4 is a top view of a prior art double rail grid;

FIGS. 5A and 5B are perspective views of a second container handlingvehicle with an exemplary lifting assembly according to the invention,with one motor on each of a first and second lifting shaft, seen fromtwo different angles;

FIGS. 5C and 5D are side views of the second container handling vehiclewith an exemplary lifting assembly according to the invention, seen fromtwo different sides;

FIG. 5E is a perspective view of the second container handling vehiclewith an exploded view of an exemplary lifting assembly according to theinvention and with one motor on each of a first and second liftingshaft;

FIGS. 6A and 6B are perspective views from the sides of the firstcontainer handling vehicle with an exemplary lifting assembly accordingto the invention;

FIGS. 6C and 6D are side views of the first container handling vehiclewith an exemplary lifting assembly according to the invention, seen fromtwo different sides;

FIG. 6E is a perspective view of the first container handling vehiclefrom above, with two motors on the same lifting shaft;

FIG. 6F is a top view of the first container handling vehicle with twomotors on the same lifting shaft;

FIG. 6G is a perspective view of the first container handling vehiclewith an exploded view of an exemplary lifting assembly according to theinvention and with two motors on one of the lifting shafts;

FIG. 6H is an upside down view of a top portion of the containerhandling vehicle according to the second embodiment;

FIGS. 7A-7F are examples of different setups of force transferringassemblies comprising guide wheel(s), lifting shaft wheels and forcetransferring element providing opposite rotation of the first and secondlifting shafts;

In the drawings, like reference numerals have been used to indicate likeparts, elements or features unless otherwise explicitly stated orimplicitly understood from the context.

DETAILED DESCRIPTION OF THE INVENTION

In the following, embodiments of the invention will be discussed in moredetail by way of example only and with reference to the appendeddrawings. It should be understood, however, that the drawings are notintended to limit the invention to the subject-matter depicted in thedrawings. Furthermore, even if some of the features are described inrelation to the system only, it is apparent that they are valid for themethods and the container handling vehicle as well, and vice versa, i.e.any features described in relation to the methods only are also validfor the system and container handling vehicle.

FIG. 3 is a top view of a grid 4 with a rail system 8 of the automatedstorage and retrieval system. The grid 4 comprises a framework structure1 comprising a plurality of upright members 2 (see FIG. 1 ) and aplurality of horizontal members 3 which are supported by the uprightmembers. As is known in the art, the upright and horizontal members maytypically be made of metal, e.g. extruded aluminium profiles. The uppersurface of the grid 4 has a rail system 8. The rail system 8 comprises afirst set of parallel tracks 10 arranged in a horizontal plane P andextending in a first direction X, and a second set of parallel tracks 11arranged in the horizontal plane P and extending in a second direction Ywhich is orthogonal to the first direction X. The first and second setsof tracks 10, 11 form a grid pattern in the horizontal plane Pcomprising a plurality of adjacent grid cells, each comprising a gridopening 12 defined by a pair of neighboring tracks 10 a, 10 b of thefirst set of tracks 10 and a pair of neighboring tracks 11 a, 11 b ofthe second set of tracks 11. The example grid openings 12 in FIGS. 3 and4 are part of the overall rail system 8 (see FIG. 1 ).

FIGS. 6A and 6B are perspective views from the sides of a firstcontainer handling vehicle with a lifting assembly according to theinvention, and FIGS. 5A and 5B are perspective views of a secondcontainer handling vehicle with an exemplary lifting assembly accordingto the invention, with one motor on each of a first and second liftingshaft, seen from two different angles.

Starting with the second container handling vehicle 9 of FIGS. 5A and5B, the container handling vehicle 9 comprises a transport mechanismexemplified as a first set of wheels 14 and a second set of wheels 15.The first set of wheels 14 and the second set of wheels are oriented inperpendicular directions such that the container handling vehicle 9 isconfigured to move on the rail system 8 above the storage columns 5,both in the X-direction and in the Y-direction. In an upper part of thecontainer handling vehicle 9, there is arranged a lifting assembly 24for picking up storage containers or bins 6 from the storage columns 5to a position above the lowest level of the first and second sets ofwheels 14, 15 on the container handling vehicle. The details of theoperation of the container handling vehicle 9 and its setup is notdescribed in greater detail herein as such container handling vehicles 9are known. The lifting assembly 24 comprises a lifting frame 18connectable to the storage container 6. The lifting frame 18 typicallycomprises a number of electrically operated grippers 38 (details ofgripper in FIGS. 5C and 5E) arranged at the circumference of the liftingframe 18, which grippers 38 grip the storage containers 6 in order tolift and move the storage containers 6 between stacks 5, to port, toanother storage system etc. A number of guiding devices 39 to guide thelifting frame 18 relative the storage containers 6 are arranged in thecorners of the lifting frame 18, on the lower surface. The lifting frame18 is lowered into the stacks and thus has a smaller cross-sectionalarea than the cells in the rail system 8.

The lifting assembly 24 further comprises a first lifting shaft 25 and asecond lifting shaft 26 of equal or near equal diameter. The first andsecond lifting shafts 25, 26 are arranged at opposite sides of thelifting assembly and are mainly parallel. Each of the first and secondlifting shafts 25, 26 are supported in an upper portion of the vehicle9. Two lifting elements, for example belts, 25′, 25″, 26′, 26″ extendfrom each of the first and second lifting shafts 25, 26 to the liftingframe 18 and is connected to the lifting frame 18 at flexible elementconnections 37 for the lifting elements (detail FIG. 5E). A motor driveassembly is connected to at least one of the first or second liftingshafts 25, 26. In FIGS. 5A and 5B the motor drive assembly comprises attwo motors 30 encircling the respective first and second lifting shafts25, 26. A force transferring assembly 32, 33′, 33″, 33′″, 33″″, 35rotatably connects the first and second lifting shafts 25, 26 via aforce transferring element 32. A tensioning mechanism, shown as atightening wheel 34, may be provided for initial tensioning of the forcetransferring element 32 in order to ensure proper force transfer and orsynchronization between the first and second lifting shafts 25, 26.FIGS. 5C and 5D are side views of the second container handling vehicle9 with an exemplary lifting assembly according to the invention, seenfrom two different sides.

FIG. 5E is a perspective view of the second container handling vehiclewith an exploded view of an exemplary lifting assembly according to oneaspect of the invention and with one motor 30 on each of a first andsecond lifting shafts 25, 26. The motor 30 is exemplified as a brushlessDC motor of the reluctance motor type, however other types of DC motorsas exemplified and described in the general part of the description canbe used instead of or in addition to the disclosed reluctance motortype, such as e.g. one or more permanent magnet motors or combinationsof different brushless DC motors. The stator 21 in the motor 30 seen inFIG. 5E is in the form of electrical windings 21 a wrapped around yokes21 b. However, a skilled person will understand that the stator 21 androtor 22 may (in other embodiments of the invention) be configured withstator magnets and rotor yokes/windings, respectively. The motor 30comprises the stator 21 arranged radially between rotor magnets (on theradial outside of the stator 21 inside wheel rim 46) and the first orsecond lifting shaft 25, 26 (on the radial inside of the stator 21). Thestator 21 is fixed to a stator housing 45, which stator housing 45 isfixedly connected to the housing of the container handling vehicle 9.The rotor magnets (not shown) are arranged on an inside of a wheel rim46 surrounding the stators 21 and is rotationally connected, for examplevia a cone bearing 44 (details of cone bearing 44 in FIG. 6G), to thefirst or second lifting shaft 25, 26 such that the rotor magnets and thefirst or second lifting shafts 25, 26 rotate together. The stator(s) 21then rotates the rotor magnets and thereby the lifting shaft 25, 26. Aprotective cover 23 encircles the wheel rim 46 and stator 21.

FIG. 5E further discloses an example of how the lifting elements 25′,26, 26′, 26″ are reeled on a reel around the first and second liftingshafts 25, 26, respectively. When the lifting shafts 25, 26 rotate, thereels rotate together with the lifting shaft 25, 26 and, dependent onthe direction of rotation, the lifting frame 18 is lifted or lowered.The lifting elements 25′, 25″, 26′, 26″ are preferably electrically andsignally conductive such that grippers 38 in the lifting frame 18 can beelectronically operated to grip and release bins or containers 6.

The force transferring assembly comprises a number of wheels 33′, 33″,33′″, 33″″, including first lifting shaft wheel 33′ and second liftingshaft wheel 33″, the wheels 33′, 33″, 33′″, 33″″ being such mutuallyarranged that when one of the first or second lifting shafts 25, 26 movein a first rotational direction the other of said first and secondlifting shafts 25, 26 moves in a second rotational direction oppositethe first direction, in both rotational directions. The first liftingshaft wheel 33′ is connected for rotation with the first lifting shaft25 and the second lifting shaft wheel 33″ is connected for rotation withthe second lifting shaft 26, and follows any rotational movement of thefirst and second lifting shafts 25, 26, respectively. At least one ofthe other guide wheels 33′″ is arranged inside the closed loop (seedetails in FIGS. 7A-7F). In addition, the first or second lifting shaftwheel 33′, 33″ is in contact with an inner surface of the endless belt32 and the other of the first or second lifting shaft wheel 33′, 33″ isin contact with the outer surface of the endless belt 32, thereby thefirst and second lifting shaft wheels 33′, 33″ (and thus the first andsecond lifting shafts 25, 26) rotates in opposite direction. Thisopposite rotation ensures that the lifting frame 18, and any storagecontainer lifted by the lifting frame 18, is lifted substantiallyvertically with minimum horizontal movement during the vertical liftingoperation. Preferably, the first and second lifting shafts 25, 26 andthe lifting elements 25′, 25″, 26′, 26″ are such connected that thelifting elements 25′, 25″, 26′, 26″ are reeled onto the first and secondlifting shafts 25, 26 from outside (see details of lifting elements 26′,26″ in FIG. 5A where it is disclosed that the lifting elements 26′, 26″extends on the outside of the second lifting shaft 26). This ensuresconnection of the lifting elements 25′, 25″, 26′, 26″ in end portions(e.g. in the corners or close to the corners) of the lifting frame 18 aswell as it ensures that the lifting frame is centred and only moves inthe vertical direction (no or minimum horizontal movement) relative thefirst and second lifting shafts 25, 26 during the entire liftingsequence.

Again, with reference to FIGS. 5A and 5D, it is further disclosed abrake arrangement 40 for the lifting shaft(s). The brake arrangement isarranged inside the container handling vehicle 9 (could also be arrangedon the outside of the container handling vehicle 9) and is disclosed aslocking pin 40′ cooperating with a gear (gear exemplified as secondlifting shaft 33″ in FIG. 5D) connected for rotation with the firstlifting shaft 25 (FIG. 5A). In a locked position of the lockingarrangement 40, the locking pin 40′ is in engagement with the gear onthe lifting shaft 25, thereby preventing rotation of the gear (and thusthe lifting shaft 25, 26). In an open position of the lockingarrangement 40, the locking pin 40′ is operated to a position out ofengagement with the gear on the lifting shaft 25, thereby the liftingshaft is free to rotate on any instructions from the motor(s) 30.

FIGS. 6A and 6B are perspective views from the sides of the firstcontainer handling vehicle with an exemplary lifting assembly accordingto the invention.

FIGS. 6C and 6D are side views of the first container handling vehiclewith an exemplary lifting assembly according to the invention, seen fromtwo different sides.

FIG. 6E is a perspective view of the first container handling vehiclefrom above, with two motors on the same lifting shaft.

FIG. 6F is a top view of the first container handling vehicle with twomotors on the same lifting shaft.

FIG. 6G is a perspective view of the first container handling vehiclewith an exploded view of an exemplary lifting assembly according to theinvention and with two motors on one of the lifting shafts.

FIG. 6H is an upside down view of a top portion of the containerhandling vehicle according to the second embodiment;

Referring to FIGS. 6B and 6H, it is, similar to FIG. 5A, disclosed abrake arrangement 40 for lifting shaft 25. The brake arrangement 40 isarranged outside the housing container handling vehicle 9 and maycomprise a locking pin 40′ cooperating with a gear connected forrotation with the first lifting shaft 25, e.g. a ratchet mechanism. In alocked position of the locking arrangement 40, the locking pin is inengagement with the gear on the lifting shaft 25, thereby preventingrotation of the gear (and thus the lifting shaft 25). In an openposition of the locking arrangement 40, the locking pin is operated to aposition out of engagement with the gear on the lifting shaft 25,thereby the lifting shaft is free to rotate on any instructions from themotor(s) 30. Furthermore, in FIG. 6H, details of the support for thelifting shafts 25, 26 and the brushes for power and signal communicationto the lifting elements for the first and second lifting shafts 25′,25″, 26′, 26″ arranged in the top portion of the container handlingvehicle (generally at 41) are disclosed. Furthermore, FIG. 6H showsdetails of a ‘key-hole’—configuration 36′, 36″ in the housing of thecontainer handling vehicle for receiving the first and second liftingshafts 25, 26. The key-hole configuration comprises a recess guidingportion 36″ with a cross section area substantially equal to thediameter of the first and second lifting shafts 25, 26. As such, thefirst and second lifting shafts can be guided into an inner recess 36′of a somewhat larger cross section area than the recess guiding portion36″. Once the respective lifting shafts 25, 26 have entered the innerrecess 36, supports 41′ of substantially equal cross section area as theinner recesses 36′ are installed from each axial end of the respectivelifting shafts 25, 26, thereby the lifting shafts 25, 26 are locked bysuitable fastening means such as threaded connection, screws or bolts 42in the inner recesses 36′ and prevented from escaping the inner recess36′ through the recess guiding portion 36″. If any repair or maintenanceof the lifting shafts are required, the fastening means 42 areunfastened, the supports 41′ removed, and the lifting shafts are free tobe removed through the recess guiding portion 36′.

Although the first and second container handling vehicles are differentwhere one has a central cavity construction for receiving storagecontainers and the other has a cantilever construction for receivingstorage containers, the lifting assembly 24 of the first containerhandling vehicle 9 is the same as the lifting assembly 24 described inrelation to the second container handling vehicle 9. Thus, thedescription of the features and functional operation of the liftingassembly 24 is the same for both container handling vehicles, and willnot be repeated.

FIGS. 7A-7F are examples of different setups of force transferringassemblies providing opposite rotation of the first and second liftingshafts 25, 26. As disclosed in all of the examples of FIGS. 7A-7F,common to all of the force transferring assemblies, is the presence of afirst and second lifting shaft wheel 33′, 33″ whereof each is connectedfor rotation with the respective lifting shaft 25, 26, at least oneother guide wheel 33′″, 33″″, a force transferring element 32 in theform of an endless belt forming a closed loop and where at least one ofthe other guide wheels 33′″, 33″″ is arranged inside the closed loop. Inaddition, the first or second lifting shaft wheel 33′, 33″ is in contactwith an inner surface of the endless belt 32 and the other of the firstor second lifting shaft wheel 33′, 33″ is in contact with the outersurface of the endless belt 32. This is achieved by arranging one of thefirst or second lifting shaft wheels 33′, 33″ inside the closed loopformed by the force transferring element 32 and the other of the firstor second lifting shaft wheel 33′, 33″ outside the closed loop formed bythe force transferring element 32. The mutual setup of the first andsecond lifting shaft wheels 33′, 33″, the guide wheels 33′″, 33″″ andthe force transferring element 32, are such that the first and secondlifting shafts 25, 26 (via first and second lifting shaft wheels 33′,33″, respectively) rotate in opposite directions (counter rotates). Thefirst and second lifting shaft wheels 33′, 33″ are preferably arrangedin the same horizontal plane in order to ensure horizontal stabilityduring lifting. The guide wheel(s) 33′″, 33″″ are arranged along thetravel of the force transferring element 32 at fixed positions such thatthey provide for a “change” in the travel direction of the forcetransferring element 32. Each of the guide wheels 33′″, 33″″ arearranged to lead the force transferring element 32 correctly onto thefirst and second lifting shaft wheel 33′, 33″ thereby allowing the firstand second lifting shaft wheels 33′, 33″ (and thus the lifting shafts25, 26) to rotate in opposite directions.

In the example in FIG. 7A, one guide wheel 33′″ is shown.

In the examples of FIGS. 7B-7F, a number of examples of forcetransferring assemblies comprising two guide wheels 33′″, 33″″, areshown. The guide wheels 33′, 33″ are arranged alternating along the pathof the force transferring element 32 such that the first lifting shaftwheel 31′ is followed by a guide wheel 33′″, 33″″ and the second liftingshaft wheel 33″ is followed by a guide wheel 33′″, 33″″ in bothdirections of travel of the force transferring element 32.

In the examples of FIGS. 7D, 7E, 7F, there are disclosed examplescomprising a tightening wheel 34 for tensioning of the forcetransferring element 32. The tightening wheel 34 may for example be aneccentric tensioning mechanism comprising a rotatable guide wheel withan axle that can be adjusted within an opening in a fixed bracket. Thelocation of the tightening wheel 34 along the path of the forcetransferring element 32 is preferably at a location where the pathlength of the force transferring element 32 can be affected (i.e. thepath of the force transferring element can be shortened or prolonged inorder to further tension or reduce tension in the force transferringelement). The tightening wheel 34 can be arranged inside (FIGS. 7D and7F) or outside (FIG. 7E) the closed loop formed by the forcetransferring element 32.

In the examples in FIGS. 7A-7C, a dedicated tensioning mechanism such asa tightening wheel is not shown; however, if a tensioning mechanism isrequired, one of the guide wheels 33′″ or 33″″ may be a tensioningmechanism and can be replaced by a tightening wheel 34.

One or more of the aspects of the invention provides for advantages overprior art, including:

-   -   The efficiency of the lift of storage containers between the        container handling vehicle and the storage columns is improved,    -   The capacity of the storage system in terms of moving more        storage containers in less time is increased,    -   The system compensates if a load of a storage container is        unequally distributed and the center of gravity of the storage        container is more to one side than another side,    -   The lifting system is easier to assemble and maintain, and        comprises fewer parts than the prior art solutions.

In the preceding description, various aspects of an automated storageand retrieval system according to the invention have been described withreference to the illustrative embodiment. However, this description isnot intended to be construed in a limiting sense. Various modificationsand variations of the illustrative embodiment, as well as otherembodiments of the system, which are apparent to persons skilled in theart, are deemed to lie within the scope of the present invention asdefined by the following claims.

LIST OF REFERENCES

 1 Framework structure  2 Upright member  3 Horizontal member  4 Storagegrid  5 Storage column  6 Storage container  7 Stack  8 Rail system  9Container handling vehicle 10 First set of rails 11 Second set of rails12 Grid column 13 Vehicle body 14 First set of wheels (transportmechanism) 15 Second set of wheels (transport mechanism) 16 Liftingdevice (elevator) 17 Connection 18 Lifting frame 19 First port column 20Second port column 21 stator  21a Windings  21b yokes 23 cover 24Lifting assembly 25 First Lifting shaft 25′, 25″ Lifting elements firstlifting shaft 26 Second Lifting shaft 26′, 26″ Lifting elements secondlifting shaft 30 Motor 32 force transferring element belt  33′ Firstlifting shaft wheel  33″ Second lifting shaft wheel 33″′, 33″″ Guidewheel 34 Tightening wheel 35 Fastening element  36′ Inner recess  36″Recess Guiding portion 37 Flexible element connections for liftingelements 38 gripper 39 Guiding device 40 Brake arrangement 41 support 44Cone bearing 45 Stator housing 46 Wheel rim

What is claimed is:
 1. An automated storage and retrieval systemcomprising: a plurality of stacks of storage containers arranged instorage columns, and a container handling vehicle comprising: atransport mechanism for transport of the vehicle, and a lifting assemblyfor picking up storage containers from the storage columns, wherein thelifting assembly comprises: a lifting frame connectable to a storagecontainer, a first lifting shaft and a second lifting shaft, the firstand second lifting shafts being mainly parallel, and each of the firstand second lifting shafts being supported in an upper portion of thevehicle, two lifting elements extending from each of the first andsecond lifting shafts to the lifting frame, and a motor drive assemblycomprising at least one motor including a first motor, and a forcetransferring assembly rotatably connecting the first and second liftingshafts via a force transferring element, wherein the force transferringelement comprises an endless belt with an inner surface and an outersurface, and wherein the first lifting shaft is in contact with one ofthe inner surface and the outer surface of the belt and the secondlifting shaft is in contact with another of the inner surface and outersurface of the belt.
 2. The automated storage and retrieval systemaccording to claim 1, further comprises a rail system comprising a firstset of parallel tracks arranged in a horizontal plane and extending in afirst direction, and a second set of parallel tracks arranged in thehorizontal plane and extending in a second direction which is orthogonalto the first direction, which first and second sets of tracks form agrid pattern in the horizontal plane comprising a plurality of adjacentgrid cells, each comprising a grid opening defined by a pair ofneighboring tracks of the first set of tracks and a pair of neighboringtracks of the second set of tracks.
 3. The automated storage andretrieval system according to claim 2, wherein the force transferringassembly comprises a first lifting shaft wheel connected for rotationwith the first lifting shaft and a second lifting shaft wheel connectedfor rotation with the second lifting shaft and at least one guide wheelurging the outer surface of the belt against one of the first or secondlifting shaft wheels, such that when one of the first or second liftingshaft moves in a first rotational direction the other of the first andsecond lifting shaft moves in a second rotational direction opposite thefirst direction, in both rotational directions.
 4. The automated storageand retrieval system according to claim 3, wherein the endless beltforms a closed loop, and wherein one of the first or second liftingshaft wheels is arranged inside the closed loop and the other of thefirst or second lifting shaft wheels is arranged outside the closedloop.
 5. The automated storage and retrieval system according to claim1, wherein the force transferring assembly comprises a tensioningmechanism for initial tightening of the force transferring element. 6.The automated storage and retrieval system according to claim 1, whereinthe at least one motor comprises a brushless DC motor.
 7. The automatedstorage and retrieval system according to claim 6, wherein the at leastfirst motor comprises a rotary electrical motor converting directcurrent electrical energy into rotational energy of the at least firstor second lifting shafts.
 8. The automated storage and retrieval systemaccording to claim 1, wherein the motor drive assembly comprises asecond motor, and wherein the force transferring assembly comprises abelt transferring torque from the first or second lifting shaft with thefirst and second motors to the other of the first or second liftingshaft.
 9. The automated storage and retrieval system according to claim1, wherein the motor drive assembly comprises a second motor, andwherein the force transferring assembly comprises a timing beltproviding synchronous movement of the first and second lifting shaftsrelative each other.
 10. The automated storage and retrieval systemaccording to claim 1, wherein a rotational force of the motor driveassembly corresponds to intended maximum weight of storage containerwith item.
 11. The automated storage and retrieval system according toclaim 1, wherein the force transferring assembly comprises a number ofangular gears and a link shaft, wherein the angular gears are connectedfor rotation with each of the first and second lifting shafts and thelink shaft is arranged between the angular gears of the first and secondlifting gears.
 12. A container handling vehicle for moving storagecontainers stacked in stacks within an automated storage and retrievalsystem, wherein the container handling vehicle is configured to moveabove storage columns and comprises: a lifting assembly for picking upstorage containers from the storage columns, wherein the liftingassembly comprises: a lifting frame connectable to a storage container,a first lifting shaft and a second lifting shaft, the first and secondlifting shafts being mainly parallel, each of the first and secondlifting shafts being supported in an upper portion of the vehicle, twolifting elements extending from each of the first and second liftingshafts to the lifting frame, a motor drive assembly comprising at leasta first motor, and a force transferring assembly rotatably connectingthe first and second lifting shafts via a force transferring element,wherein the force transferring element comprises an endless belt with aninner surface and an outer surface, and wherein the first lifting shaftis in contact with one of the inner surface and the outer surface of thebelt, and the second lifting shaft is in contact with another of theinner surface and outer surface of the belt.
 13. A container handlingvehicle according to claim 12, wherein the force transferring elementcomprises a first lifting shaft wheel connected for rotation with thefirst lifting shaft and a second lifting shaft wheel connected forrotation with the second lifting shaft and at least one guide wheel,such that when one of the first and second lifting shafts moves in afirst rotational direction another of the first and second liftingshafts moves in a second rotational direction opposite the firstdirection, wherein the endless belt forms a closed loop, and wherein oneof the first and second lifting shaft wheels is arranged inside theclosed loop and another of the first and second lifting shaft wheels isarranged outside the closed loop.
 14. Use of a container handlingvehicle according to claim 12 for storage and retrieval of storagecontainers in a storage system.
 15. A method of operating an automatedstorage and retrieval system according to claim 1, comprising providingsignals to different container handling vehicles operating in the systemto store storage containers in stacks and retrieve storage containersfrom stacks.
 16. A method of operating a lifting assembly of a containerhandling vehicle comprising: arranging a motor drive assembly comprisingat least a first motor, connecting two lifting elements from each of afirst lifting shaft and a second lifting shaft to a lifting frame, androtationally coupling the first and second lifting shafts, through aforce transferring assembly, wherein the force transferring elementcomprises an endless belt with an inner surface and an outer surface,and wherein the first lifting shaft is in contact with one of the innersurface and the outer surface of the belt and the second lifting shaftis in contact with another of the inner surface and outer surface of thebelt, the force transferring assembly being configured to synchronizeraising and lowering of opposite sides of the lifting frame, and using alifting assembly for picking up storage containers from storage columnsto a position above a lowest level of a transport mechanism on thecontainer handling vehicle.